Timing of electromagnetic switches



A. W. PAULSON ETAL TIMING 0F ELECTROMAGNETIC SWITCHES Jan. 18, 1944.

Filed Jan. 8, 1942 03 }INVENTOR5 "av/Min ATTO RNEY Patented Jan. 18,1944

TIMING OF ELECTROMAGNETIC SWITCHES Arthur Willard Paulson, Yonkers, andWilliam Henry Bruns, Lincolndale, N. Y., assignors to Otis ElevatorCompany, New York, N. Y., a corporation of New Jersey ApplicationJanuary 8, 1942, Serial No. 426,042

9 Claims.

The invention relates to the timing of electromagnetic switches.

There are various direct current control circuits for electromagneticswitches in which condensers are utilized for timing the operation ofthe switches. In some arrangements the condensers are utilized to timethe going in of the.

switch, in others the dropping out of the switch and in still others totime both the going in and dropping out of the switch. It is importantnot only that accurate and uniform timing be obtained but also that thecost of'various items employed be kept at a minimum. Paper condensersare relatively expensive while electrolytic condensers are unreliable intiming under conditions when the length oftime that the condenser isdischarged is considerable and varies.

One feature of the invention resides in a timing arrangement in whichthe parts are simple and inexpensive.

Another feature of the invention resides in the provision of a timingcircuit for an electromagnetic switch in which accurate and uniformtiming may be obtained utilizing an electrolytic condenser.

Other features and advantages of the invention will become apparent fromthe following description and appended claims.

In carrying out the invention according to the arrangement which will bedescribed, the timing condenser is in a charged state when theelectromagnetic switch controlled thereby is not operated. To operatethe switch, a circuit is completed to cause a magnetizing force to beexerted for operating the switch. At the same time, the condenser isconnected to cause by its discharge a magnetizing force to be exerted todelay the operation of the switch. In the case of certain types ofswitches, aresistance may be provided which is short circuited when theswitch contacts engage to increase the operating magnetiz-- ing force topull the switch to full operated position. This enables a smallercondenser to be utilized with such switch to obtain the desired timing.In dropping out the switch, the condenser may be recharged by a circuitwhich causes sufficient magnetizing force to be exerted to maintain theswitch operated until the charging current decreases to a certain value.If desired, the condenser may be recharged without aflecting theoperation of the switch, in which event the switch is dropped outimmediately and the charging is efiected quickly in preparation for asubsequent operation.

The single figure of drawing is a' wiring diagram of a simple circuitillustrating the control of a switch in accordance with the invention.

The switch to be controlled is designated A. The coil of this switch isconnected in series with condenser across the supply lines and This coilis tapped to provide two portions designated Aa and Ab. Anelectromagnetic switch B is provided for connecting the portion Ab ofthe switch coil across the supply lines by a circuit I0 which alsoconnects the condenser C across the portion Ad of the coil. Theconstruction of the switch is such that the portion Ab alone whenconnected across the supply lines is capable of operating the switch.For convenience the coil of switch B is illustrated as controlled bymanually operable switch H. Resistance RI is a pro-' tective resistancefor the condenser. Resistance R2 is to facilitate obtaining the desiredampere turns of coil portion Aa. Resistance R3 serves to facilitateproviding the desired number of ampere turns of coil portion Ab withoutundue heating. Resistance R4 is for adjusting the time of operation. 'Itis preferred to employ a separate protective resistance RI especiallywhere several condensers are employed in parallel as this permits eachcondenser to have its own protective resistance. However, where only onecondenser is utilized as illustrated, resistance RI may be omitted andthe right hand side of contacts Bl connected between the coil of switchA and re-' sistance R3, thereby utilizing resistance R3 also as aprotective resistance.

With switch B deenergized,. the condenser is charged with the voltage ofthe supply lines while the voltage applied to the coil of switch A iszero.

To operate switch A, manual switch II is closed causing the energizationof the coil of switch B. Switch B operates to separate contacts B I,breaking the shunt circuit for the coil of switch A and resistances R2,R3 and R4. It also engages contacts B2 which connect portion Ab of thecoil of I switch A across the supply lines in circuit with resistancesR3 and R4. The closing of these contion Ab of the coil. I This preventsthe immedi 1 ate operation of the-switch. The condenser discharges untila point is reached where the magnetizing force of coil portion Aabecomes low enoughto permit coil portion Ab to operate the resistance RIbeing of a relatively low value.

The ampere turns of the portions of the coil of switch A, the capacityof the condenser and the value of resistance R2 and the resistance ofcoil portion Aa are so coordinated and the value of resistance R4 is soadjusted as to cause the switch to operate at the expiration of thedesired time interval. With a given rate of discharge of the condenser,the time of operation of the switch may be adjusted by adjusting thevalue of resistance R4.

When switch A operates it engages 'contacts'Al to short circuitresistance R4. This arrangement is particularly desirable where switch Ais a power switch, as for example having'contacts in the lines from apower supply to a motor. Such contacts have strong contact springs whichafter the contacts engage must be compressed as the switch is pulled allthe way in. This requires a larger number of ampere turns in the coilportion Ab. By utilizing auxiliary contacts AI of the switch to shortcircuit resistance R4 at the time the contacts engage, the current isincreased in coil portion Ab to a point sufiicient to pull the switchinto fully operated position against the contact springs. A given sizecondenser may be utilized to provide the same time of operation of aswitch with heavy contact springs where contacts Al are utilized as of aswitch without such springs andwithout utilizing contacts Al. Thus,contacts Al may be omitted where the switch does not have to pull allthe way home against rela-- tively strong contact springs.

To drop out switch A, switch I I is opened causing the deenergization ofswitch B. Switch B upon dropping out separates contacts 252 to breakcircuit l0, disconnecting coil'portion Ab of switch A from the line andopening the bypass for the condenser and coil portion Aa. Switch B alsoreengages contacts BI which connects the condenser directly to thesupply lines through resistance RI. Thus condenser C rechargesimmediately and there is no tendency for coil of switch A to hold theswitch in operated condition. Therefore, switch A drops out immediately.

If it be desired to delay the dropping out of switch A, the circuitthrough contacts BI is omitted in which event, upon the dropping out ofswitch B, the condenser recharges through the coil of switch A. Thus theresistance of the coil of switch A, resistance R2 and also resistanceR4, where contacts Al are not provided, delay the charging of thecondenser so that sufilcient current flows through the coil of switch Ato maintain the switch operated. As soon as the condenser charges to acertain point this current fiow is no longer suflicient to hold switch Aoperated and it drops out.

The above described arrangement is especially suitable for controllingthe operation of accelerating switches, say for an elevator hoistingmotor. In such case switch B might be a switch which operates to connectthe motor to the supply lines or operates the same time such connectionis effected, whereas switch A might be the first accelerating switch. Insuch event contacts A2 and A3 may be utilized to control the operationof a second accelerating switch in the same manner as contacts BI and B2respectively of switch B control the operation of switch A. Contacts A4would then be utilized to control a work circuit such as effecting theshort circuiting of a resistance step in circuit with the motor. It isto be understood that the application of the above arrangement tocontrolling the operation of one or more accelerating switches is onlyillustrative and that the arrangement may be utilized for various otherpurposes.

It is seen therefore that the timing of the operation of a switch iscontrolled in a very simple and reliable manner by the discharge of acondenser to create a magnetizing force in opposition to the operatingmagnetizing force. Also a very simple and reliable control of thetimingof the dropping out of a switch is effected by utiliz-' It is tobe understood that in applying'the invention to various control systems,changes may be made with a view to adapting the invention more readilyto such systems. Other changes may also be made which do not depart fromthe spirit and scope of the invention. It is therefore intended that allmatter contained in the above description and shown in the accompanyingdrawing shall be interpreted as illustrative and not in a limitingsense.

What is claimed is:

1. An electromagnetic switch having two coil portions, a condenser,means including a direct current source of supply for causing saidcondenser to be in a charged state and both coil portions deenergizedwhen the switch is not operated, I

and means for causing excitation of one of said coil portionssufilcient'to operate said switch and for connecting said condenseracross the other coil portion to cause through the discharge of thecondenser excitation of said other coil portion so as to delay theoperation of the switch.

2. An electromagnetic switch having two coil portions, a condenser,means including a direct current source of supply for causing saidcondenser to be in a charged state when the switch is not operated, andmeans for causing excitation ofone of said coil portions sufilcient tooperate said switch and for at the same time connecting said condenseracross the other of said coil portions to cause through the discharge ofthe condenser a magnetizing force to be exerted by said other coilportion in opposition to the magnetizing force exerted by said one coilportion sufiicient to delay the operation of the switch until thecondenser discharges to a certain voltage.

3. An electromagnetic switch having two coil portions, a source ofdirect current, a condenser connected to said source so as to be in acharged state when the switch is not operated, and means for connectingto said source one of said coil portions to cause suflicient magnetizingforce to be exerted thereby for operating said switch and for at thesame time connecting said condenser across the other of said coilportions to cause through the discharge of the condenser magnetizingforce to be exerted by said other coil portion in opposition to themagnetizing force exerted by said one coil portion to delay theoperation of the switch.

'assasei 4. An electromagnetic switch having two coil portions, a sourceof direct current, a condenser connected to said source in series withsaid coil portions, and means for'connecting one of said coil portionsto said source through a circuit bypassing said condenser and the otherof said coil portions to cause the operation of said switch by said onecoil portion after a delay due to the magnetizing force exerted by saidother coil portion by the discharge of the condenser therethrough beingin opposition to the magnetizing force exerted by said one coil portion.

5. ,An electromagnetic switch having two coil portions, 9. source ofdirect current, a condenserconnected to said source so as to be in acharged state when the switch is not operated, means for connecting to,said source one of said coil por- A tions to cause magnetizing force tobe exerted by said coil portion 'suiiicient to operate said switch andfor at the same time connecting said condenser across the other of saidcoil portions to cause through the discharge of said condenser coilportion inopposition' to the magnetizing force exerted by said one coilportion to delay the opermagnetizing force to be exerted by said otheration of the switch, and a variable resistance in series with said onecoil portion for adjusting the time delay'oi said switch.

6. An electromagnetic switch having a coil, a source of direct current,a condenser connected to said source in series with-said coil, and meansfor connecting a portion of said coil to said source through a circuitby-passing said condenser to cause said coil portion to exertmagnetizing force sufflcient to operate said switch, said by-passcircuit providing a discharge path for said condenser through theremainder of said coil to cause said coil remainder to exert magnetizingiorce in opposition to the magnetizing force exerted by said portion ofsaid coil to delay the operation of the switch until the opposingmagnetizlng force decreases due to the discharge of the condenser to apoint where the net magnetizing force is sumcient to operate the switch.

7. An electromagnetic switch having a coil, a

sumcient to delay the operation of the switch until the condenserdischarges to a certain voltage.

8. An electromagnetic switch having a coil, 9. source of direct current,a condenser connected to said source in series with said coil, means forconnecting a portion of said coil to' said source through acircuitby-passing said condenser to cause said coil portion to exertmagnetizing force suiiicient to operate said switch, said by-passcircuit providing a discharge pathfor saidcondenser into the remainderof said coil to cause said coil remainder to exert a magnetizing forcein opposition to the magnetizing force exerted by said portion of saidcoil sufficient to delay the operation of the switch until the condenserdischarges to a certain voltage, and means for shunting said coil tocause the dropping out of said switch and the quick recharge ofthe-condenser.

9. An electromagnetic switch having a coil, as

source of direct current, a condenser connected in series with said coilto said source so as to be charged to the voltage of said-source, andmeans for closing a circuit which connects a portion or said coil tosaid source, said coil portion when so connected exerting sufilcientmagnetizing force to operate said switch, and which also connects saidcondenser across the remainder of said coil to cause said coil remainderto exert magnetizing force in, opposition to that of said coil portionto delay the operation oi'said switch. I

. ARTHUR WILLARD PAULSON.

WILLIAM HENRY BRUNS.

